<para>
Controls whether huge pages are requested for the main shared memory
area. Valid values are <literal>try</literal> (the default),
- <literal>on</literal>, and <literal>off</literal>. With
+ <literal>on</literal>, and <literal>off</literal>.
+ This parameter can only be set at server start. With
<varname>huge_pages</varname> set to <literal>try</literal>, the
server will try to request huge pages, but fall back to the default if
that fails. With <literal>on</literal>, failure to request huge pages
platform, is generally discouraged because it typically requires
non-default kernel settings to allow for large allocations (see <xref
linkend="sysvipc"/>).
+ This parameter can only be set at server start.
</para>
</listitem>
</varlistentry>
however, it may be useful for debugging, when the
<literal>pg_dynshmem</literal> directory is stored on a RAM disk, or when
other shared memory facilities are not available.
+ This parameter can only be set at server start.
</para>
</listitem>
</varlistentry>
<xref linkend="sql-notify"/> / <xref linkend="sql-listen"/> queue.
The default value is 1048576. For 8 KB pages it allows to consume
up to 8 GB of disk space.
+ This parameter can only be set at server start.
</para>
</listitem>
</varlistentry>
<para>
Controls the largest I/O size in operations that combine I/O, and silently
limits the user-settable parameter <varname>io_combine_limit</varname>.
- This parameter can only be set in
- the <filename>postgresql.conf</filename> file or on the server
- command line.
+ This parameter can only be set at server start.
If this value is specified without units, it is taken as blocks,
that is <symbol>BLCKSZ</symbol> bytes, typically 8kB.
The maximum possible size depends on the operating system and block
blocks to prefetch. If this value is specified without units, it is
taken as bytes.
The default is 512kB.
+ This parameter can only be set at server start.
</para>
</listitem>
</varlistentry>
</term>
<listitem>
<para>
- Record commit time of transactions. This parameter
- can only be set in <filename>postgresql.conf</filename> file or on the server
- command line. The default value is <literal>off</literal>.
+ Record commit time of transactions.
+ This parameter can only be set at server start.
+ The default value is <literal>off</literal>.
</para>
</listitem>
</varlistentry>
determines the program name used to identify
<productname>PostgreSQL</productname> messages in
the log. The default is <literal>PostgreSQL</literal>.
- This parameter can only be set in the <filename>postgresql.conf</filename>
- file or on the server command line.
+ This parameter can only be set at server start.
</para>
</listitem>
</varlistentry>
main data files, <literal>wal</literal> for WAL files, and
<literal>wal_init</literal> for WAL files when being initially
allocated.
+ This parameter can only be set at server start.
</para>
<para>
Some operating systems and file systems do not support direct I/O, so